Ionic liquids are essentially salts in a liquid state, and are described in U.S. Pat. Nos. 4,764,440, 5,104,840, and 5,824,832, for example. Ionic liquids typically melt below room temperature.
Ionic liquids have been used to catalyze a variety of hydrocarbon conversion processes, such as alkylation, isomerization, disproportionation, and the like. When ionic liquids are used to catalyze hydrocarbon conversion processes, the hydrocarbon feed and the ionic liquid catalyst are typically mixed with high shear to provide intimate contact. During the mixing, small droplets of ionic liquid become suspended in the immiscible phase, and some of these small droplets of ionic liquid remain entrained in the immiscible phase after conventional liquid-liquid phase separation by gravity. Because of the relatively high cost of ionic liquids, it is important to recover this entrained ionic liquid.
One method of recovering entrained ionic liquids is described in U.S. Pat. No. 8,067,656. The process involves coalescing ionic liquid droplets onto a coalescing material, coalescing the small droplets into larger droplets on the surface of the material, and capturing the coalesced droplets by settling to provide an ionic liquid layer. However, this method requires the use of a coalescing material.
Another method is described in U.S. application Ser. No. 14/229,462, entitled Process for Recovering Entrained Ionic Liquid from an Ionic Liquid Immiscible Phase, filed Mar. 28, 2014. The method involves contacting a hydrocarbon stream containing ionic liquid droplets with additional ionic liquid in order to increase the ionic liquid volume fraction and recover the ionic liquid droplets.
There is a need for additional methods of recovering entrained ionic liquids.